This invention relates to a subscriber loop interface circuit ("SLIC") and more specifically to a SLIC with a single power source and a voltage regulator. The SLIC provides on-hook signals such as a ringing signal and/or a caller identification signal through the speech amplifiers to the telecommunications device while the telecommunications device is on-hook while maintaining industry standard voltage limits across the terminals of the telecommunications device during all modes of operation.
A SLIC is generally employed in a subscriber loop as an interface between a subscriber network and a subscriber telecommunications device, such as a residential telephone, telephone answering machine, modem, or similar device. Generally, a subscriber loop includes a SLIC, a subscriber telecommunications device, and a pair of subscriber lines for connecting the SLIC to the subscriber telecommunications device. When a subscriber telecommunications device is in an off-hook condition, the subscriber lines, subscriber terminal device, and SLIC together may form a continuous circuit for establishing two-way communications between the SLIC and the subscriber telecommunications device.
Typically, a SLIC supplies different voltages to a telecommunications device depending on whether the telecommunications device is on-hook/off-hook, or if the telecommunications device is to ring, e.g.,to notify the telecommunications device of the presence of an incoming call. Well known industry standards set maximum limits for voltages appearing across the terminals of a telecommunications device for on-hook/off-hook conditions (approximately -56V), and ringing conditions (approximately -120 V.sub.RMS).
Prior art non-ringing SLICs for traditional POTS systems are designed to meet the above requirements by using two separate voltage sources, V.sub.BAT and V.sub.RING, that power separate circuits for on-hook/off-hook condition and for ringing conditions, as illustrated in FIGS. 1 and 2. Typically, V.sub.BAT supplies power during on-hook/off-hook conditions and V.sub.RING supplies power during ringing conditions. A switch is used to alternately connect V.sub.BAT or V.sub.RING to the telecommunications device.
FIG. 1 illustrates a typical subscriber loop of a POTS system including a non-ringing SLIC 100 which contains the on-hook/off-hook circuits. The power supply 104 ("V.sub.BAT1 ") supplies power to the non-ringing SLIC 100. The power supply 105 ("V.sub.RING1 ") supplies power to the ring generator 101 which provides the ringing signal to the subscriber phone 106. The switch 103 alternately connects the subscriber phone 106 to the non-ringing SLIC 100, thereby supplying power to the subscriber phone 106 from V.sub.BAT, and the ring generator 101, thereby supplying power to the subscriber phone 106 from V.sub.RING, in response to a signal from the ring command generator 102.
V.sub.BAT typically supplies power to the non-ringing SLIC 100 at a voltage less than the industry standard maximum voltage of approximately -56 V ("V.sub.MAX ") across the terminals of the subscriber phone 106 ("V.sub.TERM ").
FIG. 2 illustrates another well-known subscriber loop of a POTS system whose operation is essentially similar to the device in FIG. 1. Like components are given similar numbers in FIGS. 1 and 2.
Prior art ringing SLICs use two power supplies as well as complex control and selection circuits, as illustrated in FIG. 3, or a single programmable power supply, as illustrated in FIG. 4, to ensure that the correct voltage is applied to the on-hook/off-hook circuits as well as the ringing circuits without exceeding the industry standard maximum voltage limits for the on-hook/off-hook condition. However, both of these solutions are undesirable because they substantially increase the cost and complexity of the ringing SLIC.
FIG. 3 illustrates a typical subscriber loop including a ringing SLIC 210 which contains both the on-hook/off-hook circuits 203 and the ringing circuits 204. The power supply 207 ("V.sub.BAT2 ") and the power supply 208 ("V.sub.RING2 ") supply power to the ringing SLIC 210. A ringing SLIC of this type requires the addition of the control circuits 201 and the voltage select circuits 200 in order to apply the proper voltage to the subscriber phone 206 for the different operating conditions of the subscriber phone 206 without allowing V.sub.TERM to exceed V.sub.MAX.
FIG. 4 illustrates another well-known ringing SLIC 210 where the voltage select circuits 200 and V.sub.BAT2 and V.sub.RING2 are replaced by a programmable power supply 209. Like components are given similar numbers in FIGS. 3 and 4.
A ringing SLIC of the present invention avoids the problems of the prior art by using a single power source in conjunction with a voltage regulator, as illustrated in FIG. 5. The single power supply supplies sufficient voltage to provide a ringing signal to the telecommunications device during ringing conditions. The voltage regulator limits the voltage across the terminals of the telecommunications device to a predetermined value below the industry standard voltage limits during on-hook/off-hook conditions. The SLIC selectively enables or disables the speech amplifiers responsive to an external control signal that is independent of the on-hook/off-hook status of the telecommunications device. The SLIC provides on-hook signals such as a ringing signal and/or a caller identification signal through the speech amplifiers to the telecommunications device while the telecommunications device is on-hook.
Accordingly, it is an object of the present invention to obviate the above problems in the prior art and to provide a novel SLIC and method in a subscriber loop.
It is another object of the present invention to provide a novel SLIC and method which requires only one power supply.
It is yet another object of the present invention to provide a novel SLIC and method with a voltage regulator for maintaining the voltage across the telecommunications device below the industry standard maximum voltage during all modes of operation.
It is still another object of the present invention to provide a novel SLIC and method for enabling the speech amplifiers in response to an external control signal that is not a function of the off-hook status of the telecommunications device.
It is a further object of the present invention to provide a novel SLIC and method for selectively enabling the speech amplifiers to provide a ringing signal and/or a caller identification signal while the telecommunications device is on-hook.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.